1. Field of the Invention
The present invention relates to a motorized screw driving tool adapted to rotate a screw using the driving power of a motor, and more particularly to a motorized screw driving tool used for separation or mounting of tires of a vehicle or to drive a lift jack.
2. Description of the Prior Art
As well known, great force is required to separate tires of a vehicle from a body of the vehicle or to drive a lift jack used to a vehicle off of the ground. In particular, it is difficult for women and old or weak persons to carry out the task of separation tires of a vehicle or driving a lift jack.
In order to solve such a problem, a motorized screw driving tool utilizing the inertial force of a motor has recently been proposed. A representative example is disclosed in U.S. Pat. No. 4,947,939. This patent discloses the structure of a motorized screw bolt driving tool which is illustrated in FIG. 1.
As shown in FIG. 1a, the motorized screw bolt driving tool of the patent includes a motor 101, and an inertia wheel mounted around a spindle coupled to the motor 101 such that it is rotated by the motor 101. Fins 102 are mounted at one side of the inertia wheel such that they are developed by a centrifugal force of the inertia wheel. Each pin 103 is connected at one end thereof to an associated one of the fins 102 by means of a link. The other end of each pin 103 protrudes from the other side of the inertia wheel. An arch shaped brake element 104 is pivotally mounted at the other side of the inertia wheel such that its pivotal movement is prevent by the protruded ends of the pins 103.
When the motor 101 rotates at a certain velocity or more, a centrifugal force capable of developing the fins 102 is generated. In this state, one of the pins 103 is retracted, so that the arch shaped brake element 104 pivots left or right, as shown in FIG. 1b.
Accordingly, the arch shaped brake element 104, which pivots at a high velocity, enters, at one or the other end thereof, a recess formed in the spindle and strikes the spindle on the facing left or right side surface of the recess. As a result of, the spindle turns a nut, or the like, engaged in the end thereof by a strong force caused by an impact resulting from an inertial force of the arch shaped brake element 104. Thus, a force sufficiently strong to separate a tire or to drive a lift jack is obtained.
However, the conventional motorized screw bolt driving tool has a structure in which the recess of the spindle is limited in its width. For this reason, it is difficult for the arch shaped brake element to engage in the recess at one time. Furthermore, the arch shaped brake element contacts the spindle in the recess in a point contact manner. As a result, a chattering phenomenon occurs which results in an instable starting force of the spindle.
After the arch shaped brake element and spindle recess are used for a certain period of time, they are abraded at the ends thereof. This results in an increase in the chattering phenomenon.
Moreover, the conventional motorized screw bolt driving tool has a structure in which the distance A between the centers of the arch shaped brake element and spindle is short, as shown in FIG. 2. Since a power transmission is carried out with such a short distance, a chattering phenomenon occurs which prevents an effective transmission of the inertial force generated by the inertia wheel.